If something happens twice, it could be a coincidence, but if it happens three times, it's more likely to be a real trend. Interestingly enough, this type of philosophy may very well apply somewhere no one saw coming: Persona 6. While the game is not confirmed to be in development, a proper sequel with a brand new slew of characters has been tossed around a few rumor mills. A follow-up to Joker and the Phantom Thieves seems inevitable, and more of a matter of time than anything.
Of course, given the barebone account of the rumors, there's next to nothing to go on. However, both Persona 4's Yu and Persona 5's Joker share a design characteristic that, if establishing a trend, could help establish a hazy background for a Persona 6 protagonist.
Persona 5 Joker's Design, Persona 4 Yu's Design
Persona 5's Joker has a lot of symbolism behind the character. There's how Joker's fake glasses help him connect emotionally, as every time he is without them, he is internally exposed. Then, there's the name behind the idea which can be the ultimate trump card in some games, it can be something that is a wild card in some games, and more. In other words, there's depth to this character.
One that's not entirely surprising is one inspiration behind his design: a cat. As mentioned in the above video, Joker is designed with a secretive, mysterious cat in mind for Persona 5. In his lanky body type, unassuming characteristics, and simplicity with a complex notion underneath, it's clear that—at least, on the surface—how a cat could have informed his character design. At the same time, Yu Narukami from Persona 4 was designed with the classic loyal and sincere dog in mind. As easily identifiable, this could apply to the Persona 6 protagonist as well.
What This Means for the Persona 6 Protagonist
Assuming the next game takes this design approach, then it would seem that a simple household pet could inform the design of the Persona 6 protagonist as well. There's a lot of caveats to that, of course, including if Persona 6 opts for character creation instead of a fully designed character. The question under this assumption quickly becomes what type of household pet could inform this new character?
Cats and dogs are some of the most common, of course, but fish outnumber even them. There's a lot of reasons for that, but this could suggest that a Persona 6 protagonist could be more of a quiet, wallflower-type. This would provide some unique storytelling options if so, and for giggles, perhaps the protagonist would have some inclination for water as well. Another common pet is the bird, which could be a protagonist who feels caged and yearns for freedom but perhaps feel too small to do so. Capturing that in a design process is by no means a simple matter, and there's far more that could inform this decision-making process such as reptiles, rodents, and more.
Ultimately, it remains to be seen what informs the design of the Persona 6 protagonist as it could be years before another game releases. If and when it does, it may be best to keep Joker as a cat and Yu as a dog in mind when looking at the character reveal for clues.
Persona 6 is rumored to be in development.